Angular coumarin – a fumarocoumarin in
which the furan ring is at an angle to the benz-2-pyrone nucleus,
as in angelicin, usually not phototoxic

Anthocyanidins – polyhydroxyflavylium
salts; a class of coloured anthocyanin aglycones (i.e. without
sugars) formed from flavan-3,4-diols, also when proanthocyanidins
are hydrolyzed with acid (in plants not formed from
proanthocyanidins); a major determinant of flower colour;
examples of anthocyanidins are pelargonidin, cyanidin,
delphinidin, peonidin, malvidin, petunidin, and melacacidin

Anthocyanins – glycosides of
anthocyanidins; a class of flavonoids based on the cyanidin
structure, differing in the presence or absence of hydroxyl
groups by methylation or glycosylation (they have sugars at
position 3 and sometimes elsewhere), forming red, pink, purple or
blue pigments; anthocyanins are one of the two main pigment
types

Arabinose –
(C5H9O4)-OH, an aldopentose
epimeric with ribose at the 2 carbon, occurring naturally in both
D- and L-forms, widely distributed in the form of complex
polysaccharides, glycosides, and mucilages; arabinoside is a
glycoside of arabinose and occurs widely in plant species as a
component of sugars, also in gum arabic

Arabitol – the polyol form of arabinose (an
alditol)

Arachidic acid – a saturated fatty acid
present in, e.g., peanut oil

Arbutin – a benzoquinone

Aristolochic acids – a group of
phenanthrene-carboxylic acid derivatives of benzoisoquinoline
precursors

Aurones – 2-benzalcoumaran-3-ones;
golden-coloured heterocyclic flavonoids isomeric with e.g.
flavones with Z-stereochemistry at the double bond, often found
in flowers; they are anthochlors; an example is sulfuretin

Azetidine-2-carboxylic acid –
C4H7NO2, a non-protein amino
acid, an alpha-amino acid with a primary imino group (-NH) and a
carboxyl group attached to the same carbon atom